Finn was one of the eight children, seven brothers and a sister, of Árni Arnmódsson or Armódsson, a lendmann, and his wife Þora Þorsteinsdóttir (daughter of Thorstein Gallows). Finn was married to King Harald's niece Bergljót Halvdansdóttir, the daughter of Halfdan Sigurðsson (Halfdan Hadafylke) and sister of Sigurðr Sýr.